A well for producing hydrocarbons from a subterranean reservoir may extend through the reservoir in a number of orientations. Traditionally, reservoirs were accessed by drilling vertical wells. This is simple and straight-forward technique, but one which provided limited reservoir contact per well. Therefore, in order to access more of a reservoir per well, techniques and devices were developed to drill horizontal wells, i.e. turning the well from vertical to horizontal at a predetermined depth below the surface. So-called multi-lateral wells provide even greater access to—and contact with—the reservoir.
A major challenge in the production of hydrocarbons from subterranean reservoirs is to increase the ability to recover the oil that is present in the reservoir. Today, only a part of the oil in a given reservoir is actually recovered and produced before the field is shut down. There are thus strong incentives for developing new technology in order to increase production and oil recovery.
Two factors are of particular importance in order to increase production and rate of recovery from a reservoir:                obtaining maximum reservoir contact, and        preventing negative effects of gas and/or water penetration/breakthrough (commonly referred to as “coning”).        
The reservoir contact is commonly achieved by drilling a number of horizontal and/or multi-lateral wells. The negative effects of coning are commonly mitigated by so-called Inflow Control Devices (ICD) placed in the production string wall. Typically, a production string in a horizontal well comprises a large number of ICDs disposed at regular intervals along its entire length. The ICDs serve as inflow ports for the oil flowing from the reservoir (normally via the annulus between the production string and the well formation) and into the production string, and are ports having a fixed flow area. So-called autonomous ICDs (AICDs) comprise one or more valve elements and are normally open when oil is flowing through the device, but chokes the flow when and where water and/or gas enters the flow. The annulus between the production string and the casing is typically divided into zones by annulus packers, which is known in the art. One or more ICDs or AICDs are then placed in each zone.
A number of ICDs are known in the art, one being described in U.S. Pat. No. 5,435,393 (Brekke, et al.) disclosing a production pipe having a production pipe with a lower drainage pipe. The drainage pipe is divided into sections with one or more inflow restrictor devices that control the flow of oil or gas from the reservoir into the drainage pipe on the basis of calculated loss of friction pressure along the drainage pipe, the calculated productivity profile of the reservoir, and the calculated inflow of gas or water.
The state of the art also includes U.S. Pat. No. 7,857,050 B2 (Zazovsky, et al.) disclosing an apparatus for use in preventing unwanted water or gas and having a flow conduit and a structure defining a tortuous fluid path proximate the flow conduit, where the tortuous fluid path receives a flow of fluid. The tortuous fluid path is defined by at least first and second members of the structure, and the first and second members are movable with respect to each other to adjust a cross-sectional flow area of the tortuous fluid path. The cross-sectional area and hence the pressure drop can be adjusted by an external force. However, the external control and force is expensive, and the number of sections is limited.
U.S. Pat. No. 7,823,645 B2 (Henriksen, et al.) discloses an inflow control device with a gas or water shut-off feature that can be operated mechanically or hydraulically from the surface of the well. The device may include a bypass feature that allows the inflow control device to be closed or bypassed via shifting of a sleeve. The flow control device can be adaptive to changes in wellbore conditions such as chemical make-up, fluid density and temperature. The device may be configured to control flow in response to changes in gas/oil ratio, water/oil ratio, fluid density and/or the operating temperature of the inflow control device. However, the external control and force is expensive and the number of zones is limited.
Autonomous ICDs (AICDs) represent an improvement of the traditional ICDs mentioned above in that they are self-controlled, i.e. without any external power supply or control.
Examples of autonomous ICDs include US 2008/0041580 A1 (Freyer, et al.) and WO 2008/004875 A1 (Aakre, et al.). While the former describes an autonomous flow restrictor with multiple flow blocking members having a density less than that of the oil, the latter discloses an autonomous flow-control device having a movable disc which is designed to move relative to an inlet opening and thereby reduce or increase the flow-through area by exploiting the Bernoulli effect and the stagnation pressure created across the disc.
US 2011/0067878 A1 (Aadnoy) describe a flow controller having a flow restrictor and a pressure-controlled actuator connected to a valve body which in turn cooperates with a valve opening. On a closing side, the actuator communicates with fluid located upstream of the valve opening and the flow restrictor. On the opening side, the actuator communicates with a fluid located downstream of the flow restrictor and upstream of the valve opening. The actuator is provided with a piston which is separated from the well fluid by at least one diaphragm-resembling seal, specifically a diaphragm having a spring constant.
US 2008/0041582 A1 (Saetre, et al.) describes a flow control apparatus having a flow restrictor positioned in the flow path between an exterior of a tubular and its passage. The flow restrictor has an active chamber and a bypass chamber, and a bypass tubing is disposed within the bypass chamber. The bypass tubing has a constant effective flow area for allowing production fluids to enter the passage from the bypass chamber. Flow blocking members are disposed within the active chamber and cooperate with outlets of the tubular to autonomously vary an effective flow area for allowing production fluids to enter the passage from the active chamber based upon the constituent composition of the production fluids.
US 2011/0198097 A1 (Moen) discloses a valve assembly for regulating fluid flow in a horizontal wellbore. A housing is coupled to a production tubular, has a chamber which is in fluid communication through a flow channel with an inner annulus formed adjacent to the wellbore. A piston and a biasing member are disposed within the chamber, where the biasing member biases the piston into a first position. A flow path is defined within the housing and communicable with both the production tubular and the inner annulus. The flow path can include one or more nozzles disposed therein, and the piston can be configured to move between the first position allowing fluid flow through the flow path to the production tubular and a second position preventing fluid flow to the production tubular. The position is determined by the pressure drop.
US 2011/0308806 A9 (Dykstra, et al.) describes an apparatus for controlling flow of fluid in a tubular positioned in a wellbore extending through a subterranean formation. A flow control system is placed in fluid communication with a main tubular. The flow control system has a flow ratio control system and a pathway dependent resistance system. The flow ratio control system has a first and second passageway, the production fluid flowing into the passageways, where the ratio of fluid flow through the passageways relates to the characteristic of the fluid flow. The pathway dependent resistance system includes a vortex chamber with a first and second inlet and an outlet, the first inlet of the pathway dependent resistance system being in fluid communication with the first passageway of the fluid ratio control system and the second inlet being in fluid communication with the second passageway of the fluid ratio control system. The first inlet is positioned to direct fluid into the vortex chamber such that it flows primarily tangentially into the vortex chamber, and the second inlet is positioned to direct fluid such that it flows primarily radially into the vortex chamber. Undesired fluids in an oil well, such as natural gas or water, are directed, based on their relative characteristic, primarily tangentially into the vortex, thereby restricting fluid flow when the undesired fluid is present as a component of the production fluid.
A common advantage of all the above mentioned examples of AICDs it that they contribute to a more even inflow along the well path compared to nozzles in traditional ICDs. The purpose is to delay the gas and/or water breakthrough as much as possible. However, they all suffer from the disadvantage that the production is choked also for the oil. The result is an overall increase in the degree of extraction (recovery) around the wells compared with the traditional ICDs, but with a significant loss of production (barrel/day) during the initial phase of the well's lifetime.
Furthermore, solutions such as those disclosed in US 2011/0067878 and US 2011/0198097 A1 would neither choke nor close for undesired phases (gas/water) at the moment of their breakthroughs.
US 2008/0041580 A1, WO 2008/004875 A1, US 2008/0041582 A1 and US 2011/0308806 A9 all contribute to a ICD character having an autonomic ability that to a certain degree choke undesired phases, though not to the extend of coming to a full, or close to full, halt in the inflow. Publications US 2008/0041580 A1 and US 2008/0041582 A1 would, in addition, not exhibit any reversible property, that is, the ability to autonomically reopen a valve that has been shut due to entrance of undesired phases at the moment when oil again starts to flow into the well.
AICDs having the ability to autonomically close, or almost close, such undesired phases are also known in the art.
One example is found in the publication U.S. Pat. No. 7,918,275 B2 which describes an apparatus having a flow control member that selectively aligns a port with an opening in communication with a flow bore of a well bore tubular. The flow control member may have an open position and a close position wherein the port is aligned with the opening and misaligned with the opening, respectively. The flow control member moves between the open position and closed position in response to a change in drag force applied by a flowing fluid. A biasing element urges the flow control member to the open or the closed position. The apparatus may include a housing receiving the flow control member. The flow control member and the housing may define a flow space that generates a Couette flow that causes the drag force. The flow space may include a hydrophilic and/or water swellable material.
However, a major problem with the solution disclosed in U.S. Pat. No. 7,918,275 B2 is that the valve is in closed position at the time of installation, during which the fluid velocity and friction is zero. Hence, there will be no force to actuate the opening. If this problem is solved it would anyway be difficult to control the opening/closing of the valve based on the flow friction since the latter is normally small compared to the friction of the valve mechanisms. In addition, the functionality of any reversible property based of drag force/friction seems doubtful.
Another example of a document disclosing a solution for an AICD which may be autonomically closed is found in publication US 2009/0283275 A1 describing an apparatus for controlling a flow of fluid into a wellbore tubular. The apparatus includes a main flow path associated with a production control device, an occlusion member positioned along the main flow path that selectively occludes the main flow path, and a reactive media disposed along the main flow path that change a pressure differential across at least a portion of the main flow path by interacting with a selected fluid. The reactive media may be a water swellable material or an oil swellable material.
Hence US 2009/0283275 A1 will for an oil reactive material installed in the main flow path results in a higher flow resistance during throughput of desired phases such as oil relative to no reactive media. A reactive material that stops the water/gas and not the oil is unknown for the inventors. The publication does not make use of a second, pilot flow as the present invention to overcome any hindering of the main flow.
The publication U.S. Pat. No. 7,819,196 B2 also describe a flow controller having a flow restrictor and a pressure-controlled actuator connected to a valve body, which in turn cooperates with a valve opening. An osmotic cell is used to operate the actuator, which cell is being placed in the fluid flow, whereby the necessary motion of the actuator to drive a valve is achieved by utilising the osmotic pressure difference between the solution in the cell and the external fluid flow/reservoir in relation to the cell. This concept has been shown to work in accordance with its principles, exhibiting a high initial oil production while at the same time closing for undesired phases. However, the solution is dependent on a membrane that should manage the harsh well conditions (high pressure and temperature, fouling, etc.) in a satisfactory way. Such a membrane is presently not known in the field.
The purpose of the present invention is to overcome the shortcomings of the prior art and to obtain further advantages.